This invention relates to a magnetic recording apparatus, and more particularly to an apparatus in which means are provided to deal with an accidental dropout attributable to, for example, attachment or deposit of dust or like foreign matter to a magnetic floppy disk or a magnetic head thereby ensuring effective magnetic recording of a video signal on the floppy disk.
A still video recorder and an electronic still camera have been developed as magnetic recording apparatus magnetically recording still pictures on a magnetic recording medium such as a magnetic floppy disk.
In the still video recorder, a still-picture video signal is recorded on and reproduced from each of a plurality of concentric tracks formed on a small-sized magnetic floppy disk loaded in the recorder. That is, in the record mode, a video signal representing one scene is applied from an external video apparatus (for example, a video camera, a video tape recorder, a video disk recorder or a television receiver) and is allotted to one of the tracks of the floppy disk to be recorded thereon. In the playback mode, a desired video signal is reproduced from a desired track of the floppy disk, and the reproduced video signal is transmitted to an external monitoring apparatus (for example, a television receiver) to display the still picture on the screen of the monitoring apparatus.
In the electronic still camera, an optical image formed by an optical lens system is converted into an electrical image signal by a solid-state imaging device, and a video signal obtained by means such as frequency modulation of the image signal is recorded on a miniature magnetic floppy disk. In the playback mode, the mini magnetic floppy disk is loaded in a reproducing apparatus, and the recorded video signal is reproduced as a still picture on, for example, the screen of a television receiver.
In the still video recorder described above, dust or like foreign matter may temporarily attach or deposit to the recording surface of the magnetic floppy disk or to a portion of the magnetic head near its magnetic gap. A dropout occurs when a video signal is recorded on such a magnetic floppy disk or by such a magnetic head to which the dust or like foreign matter temporarily attaches or deposits. In most cases, the dust or like foreign matter providing the source of the dropout is naturally removed from the floppy disk or magnetic head after recording. It is apparent that the dropout remains still in the record on the floppy disk even when the dust or like foreign matter is removed after recording.
In the case of the electronic still camera described above, re-photographing cannot be made even if a dropout may occur due to attachment or deposit of dust or like foreign matter to a magnetic floppy disk during the process of magnetic recording. This is because the subject being photographed is moving in most cases, and the same picture cannot be taken by re-photographing, resulting in missing the chance of taking the desired picture of the subject. On the other hand, when a still picture is reproduced from a dropout-containing track of the floppy disk, degradation of the picture quality due to the presence of the dropout will be highlighted.
The inventors assumed that, among dropouts present on a magnetic floppy disk, temporary dropouts except those permanently remaining on the floppy disk generally decrease while erasing and re-recording operations are repeated a plurality of times.
This assumption is based on the finding of the tendency that, when a certain track of the floppy disk is noted, a dropout detected once on that track tends to disappear after repetition of later erasing and re-recording.
In order to confirm the above tendency, the inventors sampled magnetic floppy disks which were rejected as having dropouts in the step of inspection, and conducted the following two tests (1) and (2) on the floppy disks. In the tests, 50 tracks each having a width of 60 .mu.m were formed on each floppy disk. A 50% white-level signal was used as a signal re-recorded on the floppy disks.
(1) In the first test, changes occurring in the existing dropouts due to repeated erasing and re-recording were investigated. The results are shown in FIG. 9.
(2) In the second test, the number of times of erasing and re-recording operation required for erasing the dropouts was measured for each track. The results are shown in FIG. 10.
The data shown in FIG. 9 indicate that, in the test in which records on 67 dropout-containing tracks were erased and re-recorded, 78% of the dropouts are temporary, and the remaining 22% of the dropouts are permanent or non-erasable.
The data shown in FIG. 10 indicate the number of times of erasing and re-recording operation required until temporary dropouts present on 62 tracks could be removed. In this test, dropouts which could be removed by five times of erasing and re-recording operation were designated as temporary dropouts. It will be seen in FIG. 10 that dropouts present on 66% of the tracks were removed by the first erasing and re-recording operation.
The results shown in FIGS. 9 and 10 sufficiently support the inventors' assumption described above. In other words, the above results imply the existence of an effective measure for decreasing temporary dropouts.